Alkali-free phosphoborosilicate glass

ABSTRACT

Alkali-free phosphoboroaluminosilicate glasses are provided. The glasses include the network formers SiO 2 , B 2 O 3 , and at least one of Al 2 O 3  and P 2 O 5 . The glass may, in some embodiments, have a Young&#39;s modulus of less than about 78 GPa and/or a coefficient of thermal expansion, averaged over a temperature range from about 20° C. to about 300° C., of less than about 38×10 −7 /° C. The glass may be used as a cover glass for electronic devices or as an outer clad layer for a glass laminate.

This application claims the benefit of priority under 35 U.S.C. §119 ofU.S. Provisional Application Ser. No. 61/821,426, filed on May 9, 2013,the content of which is relied upon and incorporated herein by referencein its entirety.

BACKGROUND

The disclosure relates to glasses that do not contain alkali metals ortheir oxides. More particularly, the disclosure relates to alkali-freeglasses that are formable by down-draw processes such as slot-draw andfusion-draw techniques. Even more particularly, the disclosure relatesto alkali-free glasses that can be formed into a clad layer for a glasslaminate.

SUMMARY

Alkali-free phosphoboroaluminosilicate glasses are provided. The glassesinclude the network formers SiO₂, B₂O₃, and at least one of Al₂O₃ andP₂O₅. The glass may, in some embodiments, have a Young's modulus of lessthan about 78 GPa and/or a coefficient of thermal expansion, averagedover a temperature range from about 20° C. to about 300° C., of lessthan about 38×10⁻⁷/° C. The glass may be used as a cover glass forelectronic devices or as an outer clad layer for a glass laminate.

Accordingly, one aspect of the disclosure is to provide a glasscomprising: from about 50 mol % to about 75 mol % SiO₂; from greaterthan 0 mol % to about 20 mol % Al₂O₃; from greater than 0 mol % to about35 mol % B₂O₃; from greater than 0 mol % to about 20 mol % P₂O₅; up toabout 5 mol % MgO; up to about 10 mol % CaO; up to about 5 mol % SrO; upto about 0.5 mol % Fe₂O₃; and up to about 0.1 mol % ZrO₂, wherein theglass is substantially free of alkali metal modifiers.

A second aspect of the disclosure is to provide a glass comprising SiO₂,B₂O₃, Al₂O₃, and P₂O₅. The glass is substantially free of alkali metalmodifiers. and has at least one of a Young's modulus of less than about78 GPa and a coefficient of thermal expansion, averaged over atemperature range from about 20° C. to about 300° C., of less than about38×10⁻⁷/° C.

A third aspect of the disclosure is to provide a glass laminatecomprising a core glass and a clad glass laminated onto an outer surfaceof the core glass. The clad glass layer comprises SiO₂, B₂O₃, Al₂O₃, andP₂O₅, and is substantially free of alkali metal modifiers. The cladglass has a first coefficient of thermal expansion, averaged over atemperature range from about 20° C. to about 300° C., of less than about38×10⁻⁷/° C. and the core glass has a second coefficient of thermalexpansion, averaged over a temperature range from about 20° C. to about300° C., that is greater than the first coefficient of thermalexpansion.

A fourth aspect of the disclosure is to provide a method of making aglass. The method comprises: providing a glass melt, the glass meltcomprising SiO₂, B₂O₃, and at least one of Al₂O₃ and P₂O₅, wherein theglass melt is substantially free of alkali metal modifiers; anddown-drawing the glass melt to form the glass

These and other aspects, advantages, and salient features will becomeapparent from the following detailed description, the accompanyingdrawings, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-section view of a glass laminate.

DETAILED DESCRIPTION

In the following description, like reference characters designate likeor corresponding parts throughout the several views shown in thefigures. It is also understood that, unless otherwise specified, termssuch as “top,” “bottom,” “outward,” “inward,” and the like are words ofconvenience and are not to be construed as limiting terms. In addition,whenever a group is described as comprising at least one of a group ofelements and combinations thereof, it is understood that the group maycomprise, consist essentially of, or consist of any number of thoseelements recited, either individually or in combination with each other.Similarly, whenever a group is described as consisting of at least oneof a group of elements or combinations thereof, it is understood thatthe group may consist of any number of those elements recited, eitherindividually or in combination with each other. Unless otherwisespecified, a range of values, when recited, includes both the upper andlower limits of the range as well as any ranges therebetween. As usedherein, the indefinite articles “a,” “an,” and the correspondingdefinite article “the” mean “at least one” or “one or more,” unlessotherwise specified. It also is understood that the various featuresdisclosed in the specification and the drawings can be used in any andall combinations.

As used herein, the terms “glass article” and “glass articles” are usedin their broadest sense to include any object made wholly or partly ofglass. Unless otherwise specified, all compositions are expressed interms of mole percent (mol %) and coefficients of thermal expansion(CTE) are expressed in terms of 10⁻⁷/° C.

It is noted that the terms “substantially” and “about” may be utilizedherein to represent the inherent degree of uncertainty that may beattributed to any quantitative comparison, value, measurement, or otherrepresentation. These terms are also utilized herein to represent thedegree by which a quantitative representation may vary from a statedreference without resulting in a change in the basic function of thesubject matter at issue.

Referring to the drawings in general and to FIG. 1 in particular, itwill be understood that the illustrations are for the purpose ofdescribing particular embodiments and are not intended to limit thedisclosure or appended claims thereto. The drawings are not necessarilyto scale, and certain features and certain views of the drawings may beshown exaggerated in scale or in schematic in the interest of clarityand conciseness.

Described herein are glasses and glass articles made therefrom thatcomprise the network formers SiO₂, Al₂O₃, B₂O₃, and P₂O₅ and are free ofalkali metals and alkali metal oxides and have low (i.e., less thanabout 40×10⁻⁷/° C. when measured over a temperature range from about 20°C. to about 300° C.) coefficients of thermal expansion (CTE). Inaddition, the amount of alkaline earth oxides is also minimized in orderto further reduce the CTE of the glass. In some embodiments, theseglasses also have low values of Young's modulus and shear modulus toimprove the intrinsic or native damage resistance of the glass.

In some embodiments, the glasses described herein are formable bydown-draw processes that are known in the art, such as slot-draw andfusion-draw processes. The fusion draw process is an industrialtechnique that has been used for the large-scale manufacture of thinglass sheets. Compared to other flat glass manufacturing techniques,such as the float or slot draw processes, the fusion draw process yieldsthin glass sheets with superior flatness and surface quality. As aresult, the fusion draw process has become the dominant manufacturingtechnique in the fabrication of thin glass substrates for liquid crystaldisplays, as well as for cover glass for personal electronic devicessuch as notebooks, entertainment devices, tables, laptops, and the like.

The fusion draw process involves the flow of molten glass over a troughknown as an “isopipe,” which is typically made of zircon or anotherrefractory material. The molten glass overflows the top of the isopipefrom both sides, meeting at the bottom of the isopipe to form a singlesheet where only the interior of the final sheet has made direct contactwith the isopipe. Since neither exposed surface of the final glass sheethas made contact with the isopipe material during the draw process, bothouter surfaces of the glass are of pristine quality and do not requiresubsequent finishing.

In order to be fusion drawable, a glass must have a sufficiently highliquidus viscosity (i.e., the viscosity of a molten glass at theliquidus temperature). In some embodiments, the glasses described hereinhave a liquidus viscosity of at least about 150 kilopoise (kpoise). Insome embodiments, these glasses have a liquidus viscosity of at leastabout 300 kpoise.

Traditional fusion draw is accomplished using a single isopipe,resulting in a homogeneous glass product. The more complicated laminatefusion process makes use of two isopipes to form a laminated sheetcomprising a core glass composition surrounded on either (or both) sideby outer clad layers. One of the main advantages of laminate fusion isthat when the coefficient of thermal expansion of the clad glass is lessthan that of the core glass, the CTE difference results in a compressivestress in the outer clad layer. This compressive stress increases thestrength of the final glass product without the need for ion exchangetreatment. Unlike ion exchange, this strengthening can be achievedwithout the use of alkali ions in the glass.

Accordingly, in some embodiments, the alkali-free glasses describedherein may be used to form a glass laminate, schematically shown inFIG. 1. Glass laminate 100 comprises a core glass 110 surrounded by aclad glass 120 or “clad layer” formed from the alkali-free glassdescribed herein. The core glass 110 has a CTE that is greater than thatof the alkali-free glass in the clad layer 120. The core glass may, insome embodiments, be an alkali aluminosilicate glass. In onenon-limiting example, the core glass is an alkali aluminosilicate glasshaving the composition 66.9 mol % SiO₂, 10.1 mol % Al₂O₃, 0.58 mol %B₂O₃, 7.45 mol % Na₂O, 8.39 mol % K₂O, 5.78 mol % MgO, 0.58 mol % CaO,0.2 mol % SnO₂, 0.01 mol % ZrO₂, and 0.01 mol % Fe₂O₃, with a strainpoint of 572° C., an anneal point of 629° C., a softening point of 888°C., and CTE=95.5×10⁻⁷/° C.

When employed as a clad glass in a laminated product, the alkali-freeglass compositions described herein can provide high compressivestresses to the clad layer. The CTE of alkali-free fusion formableglasses are generally in the range of 30×10⁻⁷/° C. or less. When such aglass is paired with, for example, an alkali aluminosilicate glass(e.g., Gorilla® Glass, manufactured by Corning Incorporated) having aCTE of 90×10⁻⁷/° C., the expected compressive stress in the clad glasscan be calculated using the elastic stress equations given below inwhich subscripts 1 and 2 refer to the core glass and the clad glass,respectively:

$\sigma_{2} = \frac{E_{1}\left( {e_{2} - e_{1}} \right)}{\left( {\frac{E_{1}}{E_{2}}\left( {1 - v_{2}} \right)} \right) + \left( {\frac{2t_{2}}{t_{1}}\left( {1 - v_{1}} \right)} \right)}$and $\sigma_{1} = {{- \frac{2t_{2}}{t_{1}}}\sigma_{2}}$where E is Young's modulus, ν is Poisson's ratio, t is the glassthickness, σ is the stress, and e₂-e₁ is the difference in thermalexpansion between the clad glass and the core glass. Using the sameelastic modulus and Poisson's ratio for the clad glass and core glassfurther simplifies the above equations.

To calculate the difference in thermal expansion between the clad glassand core glass, one assumes that the stress sets in below the strainpoint of the softer glass of the clad and core. The stresses in the cladglass can be estimated using these assumptions and the equations above.For typical display-like glass with a CTE of 30×10⁻⁷/° C. as the cladglass and an alkali aluminosilicate core glass with CTE of 90×10⁻⁷/° C.,overall thicknesses in the range of 0.5-1.0 mm and clad glass thicknessof 10-100 μm, the compressive stress of the clad glass is estimated tobe in a range from about 200 MPa to about 315 MPa. As seen in Table 2below, several the alkali-free glass samples have coefficients ofthermal expansion in the range from about 15 to about 13×10⁻⁷/° C. Forthese glasses, the compressive stress of the clad glass layer would bein a range from 240 MPa to about 400 MPa.

The alkali-free glasses described herein have especially lowcoefficients of thermal expansion. In some embodiments, the CTE, whichis averaged over a temperature range from about 20° C. to about 300° C.,is less than less than 38×10⁻⁷/° C. In other embodiments the CTE of theglass averaged over a temperature range from about 20° C. to about 300°C. is less than about 20×10⁻⁷/° C. When paired with a core glass havinga higher CTE, the glasses described herein provide a high level ofcompressive stress in the clad layers of the final laminated glassproduct. This increases the strength of the glass laminate product.Room-temperature compressive stresses of at least about 100 MPa and, insome embodiments, at least about 400 MPa are attainable by using theglasses disclosed herein in the clad layer of the laminate.

The alkali-free glasses have values of Young's modulus and shear modulusthat are significantly less than those of other commercially availablefusion-drawn glasses. In some embodiments, the Young's modulus is lessthan about 78 gigapascals (GPa), in other embodiments, less than about70 GPa, and in still other embodiments, less than about 60 GPa. The lowelastic moduli provide these glasses with a high level of intrinsicdamage resistance.

In some embodiments, these alkali-free glasses have strain points ofless than 800° C.

In some embodiments, the glasses described herein consist essentially ofor comprise: from about 50 mol % to about 75 mol % SiO₂ (i.e., 50 mol%≦SiO₂≦75 mol %); from greater than 0 mol % to about 20 mol % Al₂O₃(i.e., 0 mol %<Al₂O₃≦20 mol %); from greater than 0 mol % to about 35mol % B₂O₃ (i.e., 0 mol %<B₂O₃≦35 mol %); from greater than 0 mol % toabout 20 mol % P₂O₅ (i.e., 0 mol %<P₂O₅≦20 mol %); up to about 5 mol %MgO (i.e., 0 mol %≦MgO≦5 mol %); up to about 10 mol % CaO (i.e., 0 mol%≦CaO≦10 mol %); up to about 5 mol % SrO (i.e., 0 mol %≦SrO≦5 mol %); upto about 0.5 mol % Fe₂O₃ (i.e., 0 mol %≦Fe₂O₃≦0.5 mol %); up to about0.1 mol % ZrO₂ (i.e., 0 mol %≦ZrO₂≦0.1 mol %); and, optionally, at leastone fining agent such as SnO₂, CeO₂, As₂O₃, Sb₂O₅, Cl⁻, F⁻, or the like.The at least one fining agent may, in some embodiments, include up toabout 0.7 mol % SnO₂ (i.e., 0 mol %≦SnO₂≦0.5 mol %); up to about 0.5 mol% As₂O₃ (i.e., 0 mol %≦As₂O₃≦0.5 mol %); and up to about 0.5 mol % Sb₂O₃(i.e., 0 mol %≦Sb₂O₃≦0.5 mol %).

In particular embodiments, the glasses consist essentially of orcomprise: from about 55 mol % to about 72 mol % SiO₂ (i.e., 55 mol%≦SiO₂≦75 mol %); from greater than 0 mol % to about 16 mol % Al₂O₃(i.e., 0 mol %<Al₂O₃≦16 mol %); from about 8 mol % to about 35 mol %B₂O₃ (i.e., 8 mol %≦B₂O₃≦35 mol %); from about 3 mol % to about 20 mol %P₂O₅ (i.e., 3 mol %≦P₂O₅≦20 mol %); up to about 5 mol % MgO (i.e., 0 mol%≦MgO≦5 mol %); up to about 0.2 mol % CaO (i.e., 0 mol %≦CaO≦0.2 mol %);up to about 0.2 mol % SrO (i.e., 0 mol %≦SrO≦0.2 mol %); up to about 0.1mol % ZrO₂ (i.e., 0 mol %≦ZrO₂≦0.1 mol %). The glass may further includeat least one fining agent such as SnO₂, CeO₂, As₂O₃, Sb₂O₅, Cl⁻, F⁻, orthe like. The at least one fining agent may, in some embodiments,include up to about 0.2 mol % SnO₂ (i.e., 0 mol %≦SnO₂≦0.2 mol %).

In some embodiments, the total amount of MgO, CaO, and SrO in theglasses described herein is less than or equal to about 5 mol %, inother embodiments, less than or equal to about 0.2 mol % and, inparticular embodiments, the glass is substantially free of alkalineearth modifiers.

Compositions and of non-limiting examples of these glasses are listed inTables 1a-d. Properties of examples 1-20 in Tables 1a-d are listed inTable 2. Each of the oxide components of these glasses serves afunction. Silica (SiO₂) is the primary glass forming oxide, and formsthe network backbone for the molten glass. Pure SiO₂ has a low CTE andis alkali metal-free. Due to its extremely high melting temperature,however, pure SiO₂ is incompatible with the fusion draw process. Theviscosity curve is also much too high to match with any core glass in alaminate structure. In some embodiments, the amount of SiO₂ in theglasses described herein ranges from about 50 mol % to about 75 mol %.In other embodiments, the SiO₂ concentration ranges from about 55 mol %to about 72 mol %.

In addition to silica, three network formers—Al₂O₃, B₂O₃, and P₂O₅—areincluded in the glasses described herein to achieve stable glassformation, low CTE, low Young's modulus, low shear modulus, and tofacilitate melting and forming. By mixing all four of these networkformers in appropriate concentrations, it is possible achieve stablebulk glass formation while minimizing the need for network modifierssuch as alkali or alkaline earth oxides, which act to increase CTE andmodulus. Like SiO₂, Al₂O₃ contributes to the rigidity to the glassnetwork. Alumina can exist in the glass in either fourfold or fivefoldcoordination. In some embodiments, the glasses described herein comprisefrom about 2 mol % to about 20 mol % Al₂O₃ and, in particularembodiments, from about 2 mol % to about 16 mol % Al₂O₃.

Boron oxide (B₂O₃) is also a glass-forming oxide that is used to reduceviscosity and thus improves the ability to melt and form glass. B₂O₃ canexist in either threefold or fourfold coordination in the glass networkThreefold coordinated B₂O₃ is the most effective oxide for reducing theYoung's modulus and shear modulus, thus improving the intrinsic damageresistance of the glass. Accordingly, the glasses described hereincomprise B₂O₃. In some embodiments, the glasses include up to about 35mol % B₂O₃ and, in other embodiments, from about 8 mol % to about 35 mol% B₂O₃.

Phosphorous pentoxide (P₂O₅) is the fourth network former incorporatedin these glasses. P₂O₅ adopts a quasi-tetrahedral structure in the glassnetwork; i.e., it is coordinated with four oxygen atoms, but only threeof which are connected to the rest of the network. The fourth oxygen isa terminal oxygen that is doubly bound to the phosphorous cation.Association of boron with phosphorus in the glass network can lead to amutual stabilization of these network formers in tetrahedralconfigurations, as with SiO₂. Like B₂O₃, the incorporation of P₂O₅ inthe glass network is highly effective at reducing Young's modulus andshear modulus. In some embodiments, the glasses described hereincomprise from greater than 0 mol % to about 20 mol % P₂O₅ and, in otherembodiments, from about 3 mol % to about 20 mol % P₂O₅.

Alkaline earth oxides (MgO, CaO, and SrO), like B₂O₃, also improve themelting behavior of the glass. However, they also act to increase CTEand Young's and shear moduli. In some embodiments, the glasses describedherein comprise up to about 5 mol % MgO, up to about 10 mol % CaO, andup to about 5 mol % SrO and, in other embodiments, up to about 5 mol %MgO, up to about 0.2 mol % CaO, and up to about 0.2 mol % SrO. In someembodiments, the total amount of MgO, CaO, and SrO is less than or equalto about 0.2 mol %. In other embodiments, alkaline earth oxides arepresent only in trace contaminant levels (i.e., ≦100 ppm). In stillother embodiments, the glass is substantially free of alkaline earthoxides.

The glass may also include at least one fining agent such as SnO₂, CeO₂,As₂O₃, Sb₂O₃, Cl⁻, F⁻, or the like in small concentrations to aid in theelimination of gaseous inclusions during melting. In some embodiments,the glass may comprise up to about 0.7 mol % SnO₂, up to about 0.5 mol %As₂O₃, and/or up to about 0.5 mol % Sb₂O₃. In other embodiments, atleast one fining agent may comprise up to about 0.2 mol % SnO₂.

A small amount of ZrO₂ may also be introduced by contact of hot glasswith zirconia-based refractory materials in the melter, and thusmonitoring its level in the glass may be important to judging the rateof tank wear over time. The glass, may in some embodiments, include upto about 0.1 mol % ZrO₂. The glass may further comprise lowconcentrations of Fe₂O₃, as this material is a common impurity in batchmaterials. In some embodiments, the glass may include up to about 0.5mol % Fe₂O₃.

TABLE 1a Exemplary compositions of glasses. Analyzed (mol %) 1 2 3 4 5SiO₂ 65.62 64.75 65.63 61.14 54.54 Al₂O₃ 11.91 12.27 15.86 15.96 16.16B₂O₃ 3.96 6.79 2.90 6.92 7.02 P₂O₅ 6.91 7.12 6.87 9.95 10.19 MgO 2.051.62 1.54 1.07 2.16 CaO 5.46 4.28 4.09 2.81 5.70 SrO 4.00 3.11 3.02 2.084.15 SnO₂ 0.07 0.07 0.07 0.07 0.07 Analyzed (mol %) 6 7 SiO₂ 52.45 63.65Al₂O₃ 18.71 15.75 B₂O₃ 10.02 0.04 P₂O₅ 9.91 6.89 MgO 1.57 2.05 CaO 4.177.50 SrO 3.08 4.03 SnO₂ 0.07 0.06

TABLE 1b Exemplary compositions of glasses. Batched (mol %) 8 9 10 11 12SiO₂ 60.74 62.89 64.45 64.47 66.60 Al₂O₃ 14.12 16.10 13.61 15.78 15.90B₂O₃ 6.28 0.04 0.03 0.03 2.86 P₂O₅ 8.61 7.03 8.57 6.72 6.84 MgO 1.812.13 2.04 0.10 1.56 CaO 4.87 7.73 7.37 7.05 4.06 SrO 3.49 4.01 3.86 5.772.09 SnO₂ 0.06 0.05 0.05 0.06 0.06 Batched (mol %) 13 14 15 16 17 SiO₂69.41 70.01 70.08 70.52 70.69 Al₂O₃ 17.80 17.75 15.62 13.76 11.73 B₂O₃0.04 1.92 1.87 1.85 1.92 P₂O₅ 7.05 6.66 6.87 6.71 6.73 MgO 1.60 1.021.57 2.06 2.56 CaO 2.93 1.88 2.85 3.68 4.58 SrO 1.09 0.69 1.06 1.35 1.69SnO₂ 0.06 0.06 0.06 0.07 0.06

TABLE 1c Exemplary compositions of glasses. Analyzed (mol %) 18 19 20 2122 SiO₂ 69.54 69.83 69.89 70.07 70.01 Al₂O₃ 13.66 13.70 4.00 3.84 3.89B₂O₃ 6.82 9.43 16.15 16.15 14.27 P₂O₅ 6.84 6.88 9.83 9.90 11.79 MgO 3.000.05 0.03 0.00 0.00 CaO 0.05 0.03 0.03 0.00 0.00 SrO 0.00 0.00 0.00 0.000.00 SnO₂ 0.07 0.08 0.07 0.04 0.04 Analyzed (mol %) 23 24 25 26 SiO₂69.92 71.91 70.10 66.00 Al₂O₃ 3.97 2.99 2.95 3.88 B₂O₃ 18.21 16.27 18.0520.17 P₂O₅ 7.87 8.79 8.86 9.91 MgO 0.00 0.00 0.00 0.00 CaO 0.00 0.000.00 0.00 SrO 0.00 0.00 0.00 0.00 SnO₂ 0.03 0.03 0.03 0.04

TABLE 1d Exemplary compositions of glasses. Analyzed (mol %) 27 28 29 30SiO₂ 70.00 65.44 65.59 61.51 Al₂O₃ 3.92 3.79 1.92 3.79 B₂O₃ 16.06 20.8522.81 24.78 P₂O₅ 9.88 9.83 9.57 9.83 MgO 0.04 0.02 0.03 0.02 CaO 0.020.02 0.02 0.02 SrO 0.00 0.00 0.00 0.00 SnO₂ 0.08 0.05 0.06 0.05 Analyzed(mol %) 31 32 33 34 35 SiO₂ 67.86 64.30 62.45 60.33 58.41 Al₂O₃ 3.803.81 3.83 3.83 3.85 B₂O₃ 18.39 22.05 23.76 25.86 27.71 P₂O₅ 9.88 9.789.89 9.91 9.95 MgO 0.00 0.00 0.00 0.00 0.00 CaO 0.00 0.00 0.00 0.00 0.00SrO 0.00 0.00 0.00 0.00 0.00 SnO₂ 0.07 0.07 0.07 0.07 0.07 Analyzed (mol%) 36 37 38 39 40 SiO₂ 56.09 70.61 68.58 65.70 66.00 Al₂O₃ 3.84 0.062.02 3.96 3.99 B₂O₃ 29.97 14.73 14.38 14.88 14.74 P₂O₅ 10.03 14.55 14.9715.40 15.21 MgO 0.00 0.00 0.00 0.00 0.00 CaO 0.00 0.00 0.00 0.00 0.00SrO 0.00 0.00 0.00 0.00 0.00 SnO₂ 0.07 0.05 0.06 0.06 0.06 Analyzed (mol%) 41 42 43 44 SiO₂ 69.61 69.75 61.99 62.11 Al₂O₃ 3.92 3.93 3.95 3.96B₂O₃ 16.82 16.86 30.19 30.36 P₂O₅ 9.58 9.39 3.80 3.50 MgO 0.00 0.00 0.000.00 CaO 0.00 0.00 0.00 0.00 SrO 0.00 0.00 0.00 0.00 SnO₂ 0.07 0.07 0.070.07

TABLE 2 Properties of glasses listed in Tables 1a-d. 1 2 3 4 5 AnnealPt. 784.5 759.9 802.5 774.6 718.6 (° C.): Strain Pt. 729.9 706.4 746.1718.3 671.4 (° C.): Softening Pt. 1155 1177.1 1061.8 1180.8 (° C.):Density 2.424 2.359 2.405 2.311 2.416 (g/cm³): CTE 32.7 37.5 26.9(×10⁻⁷/° C.): Poisson's 0.215 0.224 0.210 0.214 0.216 Ratio: Shear 4.1633.907 4.360 3.833 3.938 Modulus (Mpsi): Young's 10.113 9.568 10.5529.309 9.580 Modulus (Mpsi): Shear 28.70 26.94 30.06 26.43 27.15 Modulus(GPa)): Young's 69.73 65.97 72.75 64.18 66.05 Modulus (GPa): 6 7 8 9 10Anneal Pt. 815.1 724.5 713 812 793 (° C.): Strain Pt. 763.9 672.8 657758 740 (° C.): Softening Pt. 1047.4 1040 N/A 1050.9 N/A (° C.): Density2.368 2.497 2.421 2.499 2.474 (g/cm³): CTE 34.4 34.4 35.6 (×10⁻⁷/° C.):Poisson's 0.225 0.231 0.236 0.218 0.218 Ratio: Shear 4.564 3.871 3.9464.588 4.408 Modulus (Mpsi): Young's 11.181 9.533 9.756 11.171 10.734Modulus (Mpsi): Shear 31.47 26.69 27.21 31.63 30.39 Modulus (GPa)):Young's 77.09 65.73 67.27 77.02 74.01 Modulus (GPa): 11 12 13 14 15Anneal Pt. 826 801 868 843 834 (° C.): Strain Pt. 771 734 799 767 760 (°C.): Softening Pt. 1061.8 1078.8 1146 1138.5 1129.5 (° C.): Density2.529 2.385 2.373 2.342 2.346 (g/cm³): CTE 37.1 24.9 18.2 15.1 18.7(×10⁻⁷/° C.): Poisson's 0.218 0.216 0.212 0.222 0.219 Ratio: Shear 4.4854.370 4.648 4.530 4.519 Modulus (Mpsi): Young's 10.921 10.627 11.26911.067 11.015 Modulus (Mpsi): Shear 30.92 30.13 32.05 31.23 31.16Modulus (GPa)): Young's 75.30 73.27 77.70 76.30 75.95 Modulus (GPa): 1617 18 19 20 Anneal Pt. 821 796 779 743 611 (° C.): Strain Pt. 757 736707 667 549 (° C.): Softening Pt. 1052.3 (° C.): Density 2.354 2.3682.256 (g/cm³): CTE 22.5 25.7 15.7 13.7 43.7 (×10⁻⁷/° C.): Poisson's0.230 0.213 0.203 0.213 0.181 Ratio: Shear 4.354 4.312 4.044 3.761 3.369Modulus (Mpsi): Young's 10.715 10.463 9.727 9.124 7.955 Modulus (Mpsi):Shear 30.02 29.73 27.88 25.93 23.23 Modulus (GPa)): Young's 73.88 72.1467.07 62.91 54.85 Modulus (GPa): 21 22 23 24 25 Anneal Pt. 634.9 656.4584.6 625.5 612.9 (° C.): Strain Pt. 558.1 587.7 492.3 549 531.8 (° C.):Softening Pt. 1076.4 985.6 1023 976.2 993.6 (° C.): Density 2.202 2.2412.185 2.196 2.196 (g/cm³): CTE 47 34.6 54.4 42.8 43 (×10⁻⁷/° C.):Poisson's 0.19 0.21 0.22 0.19 0.22 Ratio: Shear 3.38 3.65 3.12 3.33 3.24Modulus (Mpsi): Young's 8.05 8.81 7.60 7.94 7.92 Modulus (Mpsi): Shear23.27 25.18 21.54 22.98 22.34 Modulus (GPa)): Young's 55.52 60.74 52.4154.71 54.59 Modulus (GPa): 26 27 28 29 30 Anneal Pt. 589.9 603 (° C.):Strain Pt. 508.7 556.3 640.72 643.27 604.16 (° C.): Softening Pt. 1069.81081 1068.7 996.4 1049.4 (° C.): Density 2.191 2.207 2.194 2.202 2.179(g/cm³): CTE 49.9 44.7 47.1 38.2 50.1 (×10⁻⁷/° C.): Poisson's 0.2280.197 0.217 0.215 0.231 Ratio: Shear 3.145 3.363 3.139 3.197 2.965Modulus (Mpsi): Young's 7.746 8.05 7.642 7.769 7.297 Modulus (Mpsi):Shear 21.69 23.19 21.64 22.04 20.44 Modulus (GPa)): Young's 53.41 55.5052.69 53.57 50.31 Modulus (GPa): 31 32 33 34 35 Anneal Pt. (° C.):Strain Pt. 656.64 626.12 596.12 581.75 546.89 (° C.): Softening Pt. 10771056.1 1046.9 1030.8 1015.7 (° C.): Density 2.193 2.184 2.179 2.1722.167 (g/cm³): CTE 45.3 46.9 49.3 51 50.6 (×10⁻⁷/° C.): Poisson's 0.1990.213 0.275 0.307 0.319 Ratio: Shear 3.243 3.024 2.937 2.856 2.795Modulus (Mpsi): Young's 7.779 7.339 7.488 7.465 7.372 Modulus (Mpsi):Shear 22.36 20.85 20.25 19.69 19.27 Modulus (GPa)): Young's 53.63 50.6051.63 51.47 50.83 Modulus (GPa): 36 37 38 39 Anneal Pt. (° C.): StrainPt. (° C.): 535.92 724.14 736.31 722.71 Softening Pt. 1014 1035.3 910.91093.9 (° C.): Density (g/cm³): 2.161 2.327 2.315 2.299 CTE (×10⁻⁷/°C.): 52.5 44.1 42.1 39.4 Poisson's Ratio: 0.212 0.171 0.177 0.196 ShearModulus 2.746 4.428 4.334 4.086 (Mpsi): Young's 6.655 10.372 10.2019.771 Modulus (Mpsi): Shear Modulus 18.93 30.53 29.88 28.17 (GPa)):Young's 45.88 71.51 70.33 67.37 Modulus (GPa):

A method of making the glasses described herein is also provided. themethod includes providing a glass melt comprising SiO₂, B₂O₃, and atleast one of Al₂O₃ and P₂O₅, wherein the glass melt is substantiallyfree of alkali metal modifiers, and down-drawing the glass melt to formthe glass. In some embodiments, the step of down-drawing the glasscomprises slot-drawing the glass melt and, in other embodiments,fusion-drawing the glass melt.

In certain embodiments, the method further includes providing a coreglass melt and fusion drawing the core glass melt to form a core glasshaving a coefficient of thermal expansion that is less than thecoefficient of thermal expansion of the clad glass. The clad glass meltis then fusion drawn to form the clad glass layer, thereby surroundingthe core glass. The clad glass layer is under a compressive stress of atleast about 400 MPa.

Being substantially free of alkali metals, the glasses described hereinare suitable for use in thin film transistor (TFT) display applications.These applications require an alkali-free interface, since the presenceof alkali ions poisons the thin film transistors. Thus, ion exchangedalkali-containing glasses are unsuitable for such applications. Glasslaminates that employ the alkali-free glasses described herein as a cladlayer provide a strengthened glass product combined with an alkali-freeinterface. In some embodiments, the alkali-free glasses also have highannealing and strain points to reduce thermal compaction, which isdesirable for TFT display substrates. The glasses described herein mayalso be used in color filter transistor substrates, cover glasses, ortouch interfaces in various electronic devices.

While typical embodiments have been set forth for the purpose ofillustration, the foregoing description should not be deemed to be alimitation on the scope of the disclosure or appended claims.Accordingly, various modifications, adaptations, and alternatives mayoccur to one skilled in the art without departing from the spirit andscope of the present disclosure or appended claims.

The invention claimed is:
 1. A glass, the glass comprising: from 50 mol% to 75 mol % SiO₂; from greater than 0 mol % to 20 mol % Al₂O₃; fromgreater than 0 mol % to 35 mol % B₂O₃; from 3 mol % to 20 mol % P₂O₅; upto about 5 mol % MgO; up to 10 mol % CaO; up to 5 mol % SrO; up to 0.5mol % Fe₂O₃; and up to 0.1 mol % ZrO₂ wherein: the glass comprises atleast one fining agent, the at least one fining agent comprising atleast one of SnO₂,CeO₂,Sb₂O₃, and Cl⁻; and the glass is substantiallyfree of alkali metal modifiers.
 2. The glass of claim 1, wherein theglass has a Young's modulus of less than 78 GPa.
 3. The glass of claim2, wherein the Young's modulus is less than 60 GPa.
 4. The glass ofclaim 1, wherein the glass has a coefficient of thermal expansion ofless than 38×10⁻⁷/° C. averaged over a temperature range from 20° C. to300° C.
 5. The glass of claim 4, wherein the coefficient of thermalexpansion is less than 20×10⁻⁷/° C. averaged over a temperature rangefrom 20° C. to 300° C.
 6. The glass of Claim 1, wherein the at least onefining agent comprises at least one of up to 0.7 mol % SnO₂ and up to0.5 mol % Sb₂O₃.
 7. The glass of claim 1, wherein the total amount ofMgO, CaO, and SrO in the glass is less than or equal to 0.2 mol %. 8.The glass of claim 1, wherein the glass is substantially free ofalkaline earth modifiers.
 9. The glass of claim 1, wherein the glasscomprises: from 55 mol % to 72 mol % SiO₂; from greater than 0 mol % to16 mol % Al₂O₃; from 8 mol % to 35 mol % B₂O₃; from 3 mol % to 20 mol %P₂O₅; up to 5 mol % MgO; up to 0.2 mol % CaO; up to 0.2 mol % SrO; up to0.2 mol % SnO₂; and up to 0.1 mol % ZrO₂.
 10. The glass of claim 1,wherein the glass forms a clad layer in a glass laminate comprising acore glass, wherein the core glass has a coefficient of thermalexpansion that is greater than a coefficient of thermal expansion of theclad layer.
 11. The glass of claim 10, wherein the core glass has acoefficient of thermal expansion that is greater than a coefficient ofthermal expansion of the clad layer, and the clad layer is under acompressive stress of at least 100 MPa.
 12. The glass of claim 1,wherein the glass forms at least a portion of a color filter, atransistor substrate, a cover glass, a touch interface, or combinationsthereof.
 13. The glass of claim 1, wherein the glass has a strain pointof less than 800° C.
 14. The glass of claim 1, wherein the glass has aliquidus viscosity of at least 150 kpoise.
 15. The glass of claim 14,wherein the glass is down-drawable.
 16. A glass comprising SiO₂, B₂O₃,Al₂O₃, and from 3 mol % to 20 mol % P₂O₅, wherein the glass issubstantially free of alkali metal modifiers, and wherein: the glasscomprises at least one fining agent, the at least one fining agentcomprising at least one of SnO₂, CeO₂, Sb₂O₃ , and Cl⁻; the glass issubstantially free of alkaline earth modifiers; and the glass has atleast one of a Young's modulus of less than 78 GPa and a coefficient ofthermal expansion of less than 38×10⁻⁷/° C. averaged over a temperaturerange from 20° C. to 300° C.
 17. The glass of claim 16, wherein theYoung's modulus is less than 60 GPa.
 18. The glass of claim 16, whereinthe coefficient of thermal expansion is less than 20×10⁻⁷/° C. averagedover a temperature range from 20° C. to 300° C.
 19. The glass of claim16, wherein the glass comprises: from 50 mol % to 75 mol % SiO₂; fromgreater than 0 mol % to 20 mol % Al₂O₃; from greater than 0 mol % to 35mol % B₂O₃; from 3 mol % to 20 mol % P₂O₅; up to 0.5 mol % Fe₂O₃; and upto 0.1 mol % ZrO₂.
 20. The glass of claim 19, wherein the glasscomprises: from 55 mol % to 72 mol % SiO₂; from greater than 0 mol % to16 mol % Al₂O₃; from 8 mol % to 35 mol % B₂O₃; from 3 mol % to 20 mol %P₂O₅; up to 0.2 mol % SnO₂; and up to 0.1 mol % ZrO₂.
 21. The glass ofclaim 20, wherein the at least one fining agent comprises 0.2 mol %SnO₂.
 22. The glass of claim 16, wherein the at least one fining agentcomprises at least one of up to 0.7 mol % _(SnO) ₂ and up to 0.5 mol %Sb₂O₃.
 23. The glass of claim 16, wherein the glass forms a clad layerin a glass laminate comprising a core glass, wherein the core glass hasa coefficient of thermal expansion that is greater than a coefficient ofthermal expansion of the clad layer.
 24. The glass of claim 23, whereinthe clad layer is under a compressive stress of at least 100 MPa. 25.The glass of claim 16, wherein the glass forms at least a portion of acolor filter transistor substrate, a cover glass, or a touch interface.26. The glass of claim 16, wherein the glass has a liquidus viscosity ofat least 150 kpoise.
 27. The glass of claim 26, wherein the glass isdown-drawable.
 28. The glass of claim 16, wherein the glass has a strainpoint of less than 800° C.
 29. The glass of claim 16, wherein the glasshas at least one of a Young's modulus of less than 78 GPa and acoefficient of thermal expansion of less than 20×10⁻⁷/° C. averaged overa temperature range from 20° C. to 300° C.
 30. A glass laminate, theglass laminate comprising a core glass and a clad glass laminated ontoan outer surface of the core glass, the clad glass layer comprising from50 mol % to 75 mol % SiO₂, from greater than 0 mol % to 35 mol % B₂O₃,from greater than 0 mol % to 20 mol % Al₂O₃, and from 3 mol % to 20 mol% P₂O₅, wherein: the clad glass is substantially free of alkali metalmodifiers; the glass comprises at least one fining agent, the at leastone fining agent comprising at least one of SnO₂, CeO₂, Sb₂O₃, and Cl⁻;and wherein the clad glass has a first coefficient of thermal expansionof less than 38×10⁻⁷/° C. averaged over a temperature range from 20° C.to 300° C. and the core glass has a second coefficient of thermalexpansion that is greater than the first coefficient of thermalexpansion.
 31. The glass laminate of claim 30, wherein the firstcoefficient of thermal expansion is less than 20×10⁻⁷/° C. averaged overa temperature range from 20° C. to 300° C.
 32. The glass laminate ofclaim 30, wherein the clad glass further comprises: up to 0.5 mol %Fe₂O₃; and up to 0.1 mol % ZrO₂.
 33. The glass laminate of claim 32,wherein the at least one fining agent comprises at least one of up to0.7 mol % SnO₂, and up to 0.5 mol % Sb₂O₃.
 34. The glass laminate ofclaim 32, wherein the total amount of MgO, CaO, and SrO in the glass isless than or equal to 0.2 mol %.
 35. The glass laminate of claim 32,wherein the glass comprises: from 55 mol % to 72 mol % SiO₂; fromgreater than 0 mol % to 16 mol % Al₂O₃; from 8 mol % to 35 mol % B₂O₃;from 3 mol % to 20 mol % P₂O₅; up to 5 mol % MgO; up to 0.2 mol % CaO;up to 0.2 mol % SrO; up to 0.2 mol % SnO₂; and up to 0.1 mol % ZrO₂. 36.The glass laminate of claim 30, wherein the clad glass is substantiallyfree of alkaline earth modifiers.
 37. The glass laminate of claim 30,wherein the clad glass is under a compressive stress of at least 100MPa.
 38. The glass laminate of claim 37, wherein the clad glass is undera compressive stress of at least 100 MPa.
 39. The glass laminate ofclaim 30, wherein the core glass comprises an alkali aluminosilicateglass.
 40. A method of making a glass, the method comprising: a.providing a glass melt, the glass melt comprising from 50 mol % to 75mol % SiO₂, from greater than 0 mol % to 35 mol % B₂O₃, from greaterthan 0 mol % to 20 mol % Al₂O₃, and from 3 mol % to 20 mol % P₂O₅,wherein the glass comprises at least one fining agent, the at least onefining agent comprising at least one of SnO₂,CeO₂, Sb₂O₃, and Cl⁻; andthe glass melt is substantially free of alkali metal modifiers; and b.down-drawing the glass melt to form the glass.
 41. The method of claim40, wherein down-drawing the glass melt comprises fusion-drawing theglass melt.
 42. The method of claim 41, wherein the glass melt is a cladglass melt, and wherein the method further comprises: a. providing acore glass melt; b. fusion-drawing the core glass melt to form a coreglass; and c. fusion-drawing the clad glass melt to form a clad layerglass surrounding the core glass, wherein the core glass has acoefficient of thermal expansion that is greater than that of the cladglass.
 43. The method of claim 42, wherein the clad layer is under aroom temperature compressive stress of at least 100 MPa.
 44. The methodof claim 40, wherein the glass has a coefficient of thermal expansion ofless than 38×10⁻⁷/° C. averaged over a temperature range from 20° C. to300° C.
 45. The method of claim 44, wherein the coefficient of thermalexpansion is less than 20×10⁻⁷/° C. averaged over a temperature rangefrom 20° C. to 300° C.
 46. The method of claim 44, wherein the glassfurther comprises: up to 0.5 mol % Fe₂O₃; up to 0.5 mol % SnO₂; up to0.5 mol % As₂O₃; up to 0.5 mol % Sb₂O₃; and up to 0.1 mol % ZrO₂. 47.The method of claim 46, wherein the glass comprises: from 55 mol % to 72mol % SiO₂; from greater than 0 mol % to 16 mol % Al₂O₃; from 8 mol % to35 mol % B₂O₃; from 3 mol % to 20 mol % P₂O₅; up to 5 mol % MgO; up to0.2 mol % CaO; up to 0.2 mol % SrO; up to 0.2 mol % SnO₂; and up to 0.1mol % ZrO₂.
 48. The method of claim 46, wherein the total amount of MgO,CaO, and SrO in the glass is less than or equal to 0.2 mol %.
 49. Themethod of claim 40, wherein the glass has a Young's modulus of less than78 GPa.
 50. The method of claim 49, wherein the Young's modulus is lessthan 60 GPa.
 51. The method of claim 40, wherein the glass melt issubstantially free of alkaline earth modifiers.
 52. A glass, the glasscomprising: from 50 mol % to 75 mol % SiO₂; from greater than 0 mol % to20 mol % Al₂O₃; from greater than 0 mol % to 35 mol % B₂O₃; greater than0 mol % to 20 mol % P₂O₅; and a total amount of MgO, CaO, and SrO ofless than or equal to 0.2 mol %, wherein: the glass comprises at leastone fining agent, the at least one fining agent comprising at least oneof SnO₂, CeO₂, Sb₂O₃, and Cl⁻; and the glass is substantially free ofalkali metal modifiers.